The present invention relates to a device for controlling an internal combustion engine. More specifically, the invention relates to a device for controlling an internal combustion engine which estimates a future value of a degree of opening of the engine throttle valve after a predetermined time lapses by delaying the start of operation for controlling a degree of opening of the engine throttle valve to a target value and, based on this estimated value of the degree of opening of the throttle valve, precisely estimating the amount of the intake air taken into the engine in the future.
There has been known a device for controlling an internal combustion engine including a so-called electronically controlled throttle valve of which the opening degree can be controlled independently of the amount of accelerator pedal operation by the driver and precisely estimating the amount of the air that will be taken in by the engine by delaying the start of the operation for controlling the throttle valve opening degree to a target value determined from the amount of accelerator pedal operation by a predetermined delay time.
In general, there has been employed a so-called air amount-based fuel amount control system in which the amount of the air taken in by the internal combustion engine is first measured, and the amount of fuel injection is controlled based on the measured air amount so that the engine air-fuel ratio becomes an optimum value. In such an engine, it is important to precisely measure the amount of the air taken in by the engine. In a state where the amount of the air taken in by the engine is varying due to changes in the throttle valve opening degree and in the rotational speed as a result of transient operation condition, however, it often becomes difficult to precisely measure the amount of the air taken in by the engine. The amount of the air actually taken in by the cylinders of the engine is determined at the time when the intake valves of the respective cylinders close. In order to precisely set the amount of fuel injection, therefore, the amount of fuel injection must be set based upon the amount of the air taken in by the engine at a moment when the intake valve of the cylinder closes. Generally, however, the timing for calculating the amount of fuel injection for each cylinder precedes the timing at which the intake valve closes. In order to precisely set the amount of fuel injection based on the amount of the air actually taken in by the cylinder, therefore, it is necessary to precisely estimate the amount of the air taken in by the engine at a moment when the intake valve will be closed in the future at a moment of calculating the amount of fuel injection.
The amount of the air taken in by the engine varies depending upon the throttle valve opening degree and the rotational speed of the engine. Since the rate of change in the throttle valve opening degree is relatively larger than a rate of change in the engine rotational speed during the transient operation, if the throttle valve opening degree at the time when the intake valve is closed could be precisely estimated, then, the amount of the air taken in by the engine at the time when the intake valve is closed can be estimated. In an engine equipped with an electronically controlled throttle valve which can be operated independently of the acceleration pedal operation by the driver, there has been proposed a so-called phase-advanced inverse calculation method in which the future throttle valve opening degree is precisely estimated by delaying the operation of opening or closing of the throttle valve by a predetermined period of time and the amount of the air that will be taken in by the engine in the future (amount of the air taken in by the engine when the intake valve closes in the cylinder) is precisely estimated based on the estimated throttle valve opening degree.
A device for controlling an internal combustion engine by estimating the intake air amount of this kind has been disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 10-169469.
According to the device of this publication, the target opening degree of the electronically controlled throttle valve is set based upon the present amount of accelerator pedal operation (amount of depression). However, the throttle valve is not driven to a target opening degree immediately after the target opening degree is set. Instead, the throttle valve is driven after a predetermined delaying time elapses. In general, the electronically controlled throttle valve involves a lag in operation due to the delay in the control operation or due to the delay in the activation of the mechanism. Even when the target opening degree has rapidly (e.g., stepwise) changed, therefore, there occurs a delaying time determined from the operation characteristics of the throttle valve until the throttle valve opening degree actually arrives at the target opening degree. Therefore, if the operating characteristics of the throttle valve are precisely known, it becomes possible to calculate the throttle valve opening degree at each moment until the throttle valve actually arrives at a target opening degree even when the target opening degree of the throttle valve varies stepwise. In theory, it is possible to estimate the throttle valve opening degree at each moment based on the operating characteristics of the throttle valve at a moment when the target opening degree has changed stepwise.
In actual operation, however, when the accelerator pedal is moved a large amount by the driver and the target opening degree changes continuously, a change in the target opening degree after the, moment of estimation is not reflected on the estimated value even when the future throttle valve opening degree is estimated at each moment based on the throttle valve operation characteristics at a given moment. Therefore, the estimated throttle valve opening degree loses precision.
According to the device of the above publication, after the target opening degree has been set, the start of the operation for driving the throttle valve depending upon the target opening degree is delayed by a predetermined delay time (a period of the delay time is so short that the driver does not actually feel the delay), so that a change in the target opening degree is completely reflected on the estimated throttle valve opening degree. Namely, in the device of the above publication, the actual operation of the throttle valve is delayed by the above delay time to after the change in the target opening degree. This, in other words, makes it possible to know exactly, at a moment when the throttle valve actually starts operating, how the target throttle valve opening degree will change thereafter. It is, therefore, made possible to completely reflect a change in the target opening degree on the estimated throttle valve opening degree and, hence, to precisely estimate an actual change in the throttle valve opening degree. According to the device of the above publication, the throttle valve opening degree at a moment when the intake valve closes is precisely estimated at a moment when the amount of fuel injection is calculated, and the amount of the air taken in by the engine at a moment when the intake valve closes is calculated based on this estimated throttle valve opening degree.
When applied to a fixed-valve-timing engine in which the intake and exhaust valves have fixed opening/closing timings, the device of the above publication makes it possible to precisely estimate the amount of the air taken in by the engine. However, when applied to a variable-valve-timing engine in which the timings for opening and closing the intake and exhaust valves are varied depending upon the engine operating conditions, the device of the above publication is not capable of precisely estimating the amount of the air taken in by the engine.
In the variable-valve-timing engine, the target valve timing is set depending upon the engine load (amount of the air taken in by the engine and the rotational speed). However, the amount of the air taken in by the engine is not exclusively determined by the throttle valve opening degree and the rotational speed, but varies in accordance with a change in the valve timing. Therefore, if the amount of the air taken in by the engine is estimated relying on the estimated throttle valve opening degree only as is done by the device of the above-mentioned Japanese Unexamined Patent Publication (Kokai) No. 10-169469, the accuracy of the estimation of the amount of the air taken in by the engine greatly drops when the valve timing changes.
In this case, the operating speed of the variable-valve-timing mechanism is usually considerably slower than the operating speed of the electronically controlled throttle valve. When the throttle valve opening degree changes rapidly, therefore, a change in the engine valve timing when the throttle valve opening degree is changing is negligibly small, and the precision for estimating the amount of the air taken in by the engine is not much affected. At the time of slow acceleration or slow deceleration in which the change in the throttle valve opening degree is relatively small, however, a change in the valve timing during the throttle valve opening degree is changing becomes relatively large, and the precision for estimating the amount of the air taken in greatly decreases.
In the device of the above-mentioned publication, further, the delay from when the target opening degree changes to when the throttle valve operates correspondingly is kept constant. Therefore, the timing for starting the operation of the throttle valve as viewed from the stroke cycle of each cylinder varies depending upon the timing of change in the target opening degree. In an actual internal combustion engine, the amount of the air actually taken in by the cylinder varies to some extent depending upon at which portion of the stroke cycle of the cylinder the amount of the air taken in by the engine has changed (i.e., at which portion the throttle valve opening degree has changed). Therefore, when the throttle valve opening degree starts changing on the stroke cycle of the cylinder as is done in the device of the above publication, the amount of the air actually taken in by the cylinder often changes even though the amount of the air taken in by the engine remains the same when the intake of the cylinder valve closes. This causes a decrease in the precision of estimating the amount of the air taken in by the cylinder.
It is an object of the present invention to provide a device for controlling an internal combustion engine which makes it possible to precisely calculate the amount of the air taken in by the cylinder by solving the above-mentioned problems.
According to the present invention, there is provided a device for controlling an internal combustion engine which sets a target throttle valve opening degree of the internal combustion engine based on a present amount of accelerator pedal operation and, after a predetermined delay time has passed, starts driving the throttle valve so that the actual throttle valve opening degree becomes said target opening degree, thereby to estimate the actual throttle valve opening degree in the future after a predetermined period of time has passed from the present based on said target opening degree, said delay time and the operation characteristics of the throttle valve, and to calculate the amount of the air that will be taken in by the engine in the future after said predetermined period of time has passed based upon said estimated value, said device for controlling an internal combustion engine comprising:
target valve timing-setting means for setting a target valve timing of the engine based on an actual throttle valve opening degree;
variable valve timing means for controlling the valve timing of the engine to said target valve timing
valve timing-estimating means for calculating an estimated value of said target valve timing in the future, after said predetermined period of time has passed, based on said estimated throttle valve opening degree, and for estimating an actual engine valve timing in the future after the passage of said predetermined period of time based on said estimated target valve timing; and
intake air amount-estimating means for estimating the amount of the air that will be taken in by the engine in the future after said predetermined period of time has passed based on said estimated throttle valve opening degree and said estimated valve timing.
That is, the present invention estimates not only the throttle valve opening degree but also the engine valve timing at the same time at a moment in the future.
A target value of the engine valve timing is, usually, set based on the amount of the air actually taken in by the engine and the engine rotational speed. As explained before, however, the amount of the air taken in by the engine also varies depending upon the valve timing. It is, therefore, difficult to precisely estimate both the amount of the air taken in by the engine and the valve timing. In the present invention, the target valve timing is determined based, for example, upon the throttle valve opening degree without using the amount of the air taken in by the engine that varies due to the valve timing. It is therefore made possible to estimate a target valve timing at a moment in the future by using the estimated throttle valve opening degree. If the target valve timing could be measured at a moment in the future, the actual valve timing at a moment in the future can be estimated based on the operation characteristics of the variable valve timing means by using the same method as the one used for estimating the actual throttle valve opening degree. According to the present invention, therefore, it is possible to estimate the throttle valve opening degree as well as the valve timing at a moment in the future (e.g., at a moment when the intake valve of the cylinder closes), and the amount of the air taken in by the engine is precisely calculated reflecting a change in the valve timing.
According to another aspect of the present invention, there is provided a device for controlling an internal combustion engine which sets a target throttle valve opening degree of the internal combustion engine based on a present amount of accelerator pedal operation and, after a predetermined delay time has passed, starts driving the throttle valve so that the actual throttle valve opening degree becomes said target opening degree, thereby to estimate the actual throttle valve opening degree in the future after a predetermined period of time has passed from the present based on said target opening degree, said delay time and the operation characteristics of the throttle valve, and to calculate the amount of the air that will be taken in by the engine in the future after said predetermined period of time has passed based upon said estimated value, said device for controlling an internal combustion engine comprising:
delay time-setting means for so setting said delay time that said throttle valve starts driving at a predetermined timing in a stroke of a particular cylinder of the engine.
That is, according to this aspect of the invention, the delay time is so set that the throttle valve is driven so as to be adjusted to the target throttle valve opening degree at a predetermined timing in a stroke of a particular cylinder (e.g., first cylinder). Therefore, the throttle valve starts operating whenever the engine cranks haft arrives at a predetermined rotational angular position. In the actual, internal combustion engine as described earlier, the amount of the air actually taken in by the cylinder slightly differs depending on at what portion of the stroke cycle of the cylinder the amount of the air taken in by the engine has changed (i.e., at what portion the throttle valve opening degree has changed). Therefore, when the throttle valve opening degree starts changing on the stroke cycle of the cylinder, the amount of the air actually taken by the cylinder often changes even though the amount of the air taken in by the engine is the same at a moment when the intake valve of the cylinder closes, causing a decrease in the precision of estimating the amount of the air taken in by the cylinder. In the present invention, the throttle valve opening degree always starts changing at a predetermined crank angle. The air starts to be taken in by the engine always at the same position of the stroke cycle of each cylinder. Therefore, a dispersion in the amount of the air taken in, that is caused by a change in the position where the throttle valve opening degree starts changing, does not occur and, hence, the precision for estimating the amount of the air that is taken in is improved
According to another aspect of the present invention, there is provided a device for controlling an internal combustion engine which sets a target throttle valve opening degree of the internal combustion engine based on a present amount of accelerator pedal operation, starts driving the throttle valve, after a predetermined delay time has passed, so that the actual throttle valve opening degree becomes said target opening degree, thereby to estimate the actual throttle valve opening degree in the future after a predetermined period of time has passed from the present based on said target opening degree, said delay time and the operation characteristics of the throttle valve and to calculate the amount of the air that will be taken in by the engine in the future after said predetermined period of time has passed based upon said estimated value, said device for controlling an internal combustion engine, comprising:
delay time-setting means for so setting said delay time that said throttle valve starts driving at a predetermined timing in a stroke of a particular cylinder of the engine when the engine is idling;
stall-avoiding means for avoiding an engine stall by setting a target throttle valve opening degree irrespective of the amount of accelerator pedal operation when it is probable that the engine that is idling may stall; and
means for starting the driving of the throttle valve so that the throttle valve opening degree readily reaches said target opening degree when the target throttle valve opening degree is set by said stall-avoiding means to avoid an engine stall irrespective of the delay time set by said delay time-setting means.
According to this embodiment of the invention, the throttle valve is readily driven without setting a delay time when the throttle valve is driven (throttle valve opening degree is increased) to prevent the engine that is idling from stalling due to worsening of combustion or the like. When the rotational speed of the engine that is idling greatly drops due to worsening of combustion or the like, the throttle valve opening degree must be increased as quickly as possible to avoid an engine stall. In such a case, a lagging start of operation of the throttle valve may cause the engine to stall when the engine rotational speed greatly drops since a change in the throttle valve opening degree does not occur in time. According to the present invention, therefore, when the throttle valve opening degree is increased to prevent the engine that is idling from stalling, the throttle valve opening degree is readily increased without providing a delay time thereby to prevent an engine stall.